Brian,
I agree. I'd try water instead of skim milk - and see if there's an improvement. It's all about trial and error, since everyone is different.
Real sugar, equal and splenda work fine for me. Stevia is okaytoo, but I don't like its taste. Sugar alcohols, like sorbitol are the devil.
Skim milk and skim milk powder wreak havoc. Half and half, and full whipping cream are fine. Nonfat yogurt, devil. Full fat yogurt is fine. Most grains and starches are awful for me, but corn and potatoes are fine. Movie theater popcorn is a disaster, homemade popcorn is fine. (I'm guessing the movie theater version has skim milk powder in it.)
Everything goes down better with fat.